5.8 : Taints & Tolerations (Node Repellents)

https://drive.google.com/file/d/1DNe7iyLlQPbU4PW9600TDdlNdL00FLo6/view?usp=sharing

🔍 YAML Breakdown

apiVersion: v1
kind: Pod
metadata: 
  name: nnwebserver
  namespace: learning
spec:
  containers:
    - name: nnwebserver
      image: nginx
      resources:
        requests:
          cpu: "500m"
          memory: "128Mi"
        limits:
          cpu: "1000m"
          memory: "256Mi"
      ports:
        - containerPort: 80
          name: http
          protocol: TCP
  tolerations:
  - key: "color"
    operator: "Equal"
    value: "pink"
    effect: "NoSchedule"

🔑 Key Concept:

Taints are applied to nodes → repel Pods

Tolerations are defined in Pods → allow them to tolerate taints

💡 Your Pod says:

"I can run on nodes tainted with color=pink:NoSchedule."

📌 How Taints Work

Taint Format	Meaning
`key=value:effect`	Standard taint
Effects
`NoSchedule`	❌ New Pods won’t be scheduled here (unless they tolerate)
`PreferNoSchedule`	🟡 Scheduler will try to avoid (soft rule)
`NoExecute`	⚠️ Evict existing Pods that don’t tolerate (after grace period)

✅ In your case:

Node has: color=pink:NoSchedule

Pod has toleration for color=pink:NoSchedule → ✅ Pod can be scheduled on that node

❗ Clarifying the Comment Misconception

📝 Comment says:

"Our pod can also go to other nodes that are NEUTRAL to taint... nodeone will accept ONLY pods with pink toleration."

✅ Partially correct, but incomplete:

Taints do NOT restrict a node to ONLY tolerant Pods
They only repel non-tolerant Pods
Tolerant Pods can still run on untainted nodes!

🎯 Correct Behavior:

Untainted node: Accepts any Pod (tolerant or not)

Tainted node: Accepts only Pods that tolerate the taint

💡 To force a Pod onto a tainted node, combine with nodeAffinity:

spec:
  affinity:
    nodeAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
        nodeSelectorTerms:
        - matchExpressions:
          - key: kubernetes.io/hostname
            operator: In
            values: [k3s-gpu-node]
  tolerations:
  - key: "type"
    operator: "Equal"
    value: "gpu"
    effect: "NoSchedule"